Hydrochloric Acid → Isopropyl hydrogen 1,3-dithiol-2-ylidenemalonate

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Reaction Steps

After 14.4 g (0.05 mol) of diisopropyl 1,3-dithiol-2-ylidenemalonate was dissolved in 50 ml of isopropanol, 2.95 g (0.074 mol) of sodium hydroxide aqueous solution was dropwise added to the solution at 30° C. The mixture was stirred for an hour and the resulting potassium salt was dissolved in 50 ml of water. The solution was acidified with 6N hydrochloric acid and the aqueous phase was extracted with dichloromethane. The organic phase was washed with water. After drying, the organic phase was concentrated under reduced pressure. The precipitated crystals were filtered to give 8.5 g (yield 70%) of isopropyl hydrogen 1,3-dithiol-2-ylidenemalonate as white crystals. Then, 2.7 g (0.011 mol) of the thus obtained crystals, 3.6 g (0.012 mol) of 2-chloro-1-methylpyridium p-toluenesulfonate were dissolved in 20 ml of dichloromethane. To the solution was dropwise added a solution of 0.51 g (0.011 mol) of ethanol and 3.46 g (0.034 mol) of triethylamine at 10° C. The mixture was stirred at room temperature for 2 hours. After the reaction solution was poured onto ice water followed by extraction with dichloromethane. The extract was washed successively with 2N hydrochloric acid, 10% sodium carbonate solution and then water. After drying over magnesium sulfate, the solvent was distilled off under reduced pressure. The residue was purified by silica gel column chromatography (n-hexane: ethyl acetate=2:1) to give 1.0 g (yield 35%) of the objective product. Synthesis Examples 4 to 8

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